The purpose of the proposed research is to characterize pulmonary gas exchange as assessed by the matching of alveolar ventilation and pulmonary perfusion in newborns, with nornal and diseased lungs. These studies will test the effects of infusions of drugs which alter pulmonary vascular pressure and resistance; the studies will also examine the effects of high frequency oscillatory ventilation on gas exchange in newborns treated with vasoactive agents. The mechanism of action by which vasoactive substances interact to produce changes in distribution of pulmonary blood flow will be examined using appropriate combinations of vasoactive agonists and antagonists. The proposed studies should contribute to a more precise understanding of the control of ventilation-perfusion matching, the most relevant index of pulmonary gas exchange, in the developing lung.